Biodegradable plastics have attracted attention from the standpoint of the prevention of environmental destruction, because they are decomposed by the action of microorganisms and the like in, for example, soil. Compared to general persistent plastics, biodegradable plastics were once more expensive and inferior in performance; however, biodegradable plastics overcame such drawbacks and are now being used in practical application. Demand has increased for mass production technologies for biodegradable plastics along with an increase in the usage of biodegradable plastics.
Polyhydroxyalkanoates, which are a type of biodegradable plastic, are produced by a wide range of bacteria, such as hydrogen bacteria (Ralstonia), cyanobacteria, and methanotrophs, under conditions lacking some kinds of nutrients (nitrogen, phosphorus, etc.).
Meanwhile, halobacteria reportedly accumulate a remarkable amount of PHB in the bacterial cells when grown in a medium with a pH of 7.5 to 8.56 using glucose and the like as the primary carbon source and containing a small amount of peptone and/or yeast extract (for example, see Non-Patent Documents 1 and 2).    Non-Patent Document 1: Quillaguaman J., Munoz M., Mattiasson B., Hatti-Kaul R., “Optimizing conditions for poly(beta-hydroxybutyrate) production by Halomonas boliviensis LC1 in batch culture with sucrose as carbon source.”, Appl Microbiol Biotechnol. 2007; 74(5): 981-986    Non-Patent Document 2: Quillaguaman J., Hashim S., Bento F., Mattiasson B., Hatti-Kaul R., “Poly(beta-hydroxybutyrate) production by a moderate halophile, Halomonas boliviensis LC1 using starch hydrolysate as substrate.”, J Appl Microbiol. 2005; 99(1): 151-157